Dental Conference - MID Dental Plaque Biofilm September 30, 2004

Infection as an interaction between organisms SPECIFIC INTERACTION OF MOLECULES WITH EACH OTHER. Interacting molecules interact as pairs, one of which is called the LIGAND and the other the RECEPTOR.

Symbiosis

Dental disease as an infectious disease Understanding microbial etiology  Pathogenicity (virulence) of pathogens Virulence factors  Understanding microbial pathogenesis Genetic and Molecular Basis for Virulence Understanding host response  Outcome of disease Applying to diagnosis, treatment, prevention

Dental Caries Demineralization of the tooth surface caused by bacteria

Periodontal Disease

Virulence factors Gene products that enhance a microorganism’s potential to cause disease Involved in all steps of pathogenicity  Attach to or enter host tissue  Evade host responses  Proliferate  Damage the host  Transmit itself to new hosts Encoded by virulence genes

Identifying virulence factors Microbiological and biochemical studies  In vitro isolation and characterization  In vivo systems Genetic studies  Study of genes involved in virulence  Genetic transmission system  Recombinant DNA technology Isogenic mutants A molecular form of Koch’s postulates (Falkow)

Specific Virulence Factors Adherence and Colonization Factors Invasion Factors Capsules and Other Surface Components Endotoxins Exotoxins Siderophores

Etiology of dental disease is Dental Plaque

Removal of plaque and calculus

Dental plaque as a biofilm

Definition of biofilm Matrix-enclosed bacterial populations adherent to each other and/or to surfaces or interfaces May form on a wide variety of surfaces, living tissues, indwelling medical devices, water system piping, natural aquatic systems Prevailing microbial lifestyle (vs. planktonic) Like a complex, highly differentiated, multicultured community Of single or multi-species

Biofilm: analogy to city Planktonic (nomad) vs biofilm (city) Initial colonization followed by lateral spread, vertical direction growth Shared resources and activites only possible through biofilm Protection from other species, host, and harsh environment Need communication – quorum sensing, exchange of genetic information

The nature of biofilms Natural method of growth for microorganisms Provides advantages for colonizing species  Protection from Competing microorganisms Environmental factors, host defense Toxic substances, such as lethal chemicals, antibiotics  Facilitate processing and uptake of nutrients, cross- feeding, removal of harmful metabolic products  Development of an appropriate physico-chemical environment

Formation of dental plaque ¶Acquired pellicle formation  Adherence of salivary glycoprotein on tooth surface ·Rapid colonization by pioneer species (Gram (+) cocci and rods)  S. sanguis, S. oralis, S. mitis, A. viscosus can adhere to pellicle by specificity  Resisting shear force (saliva) and electrostatic repulsion ¸Predominance by Gram (-) filaments (in 5 days)  Microbial interaction, replacing Gram (+) cocci and rods  Emergence of Gram (-) filamentous bacteria  Matrix of microorganisms and a ground substance

Climax Community Dental pellicle

Structure of biofilms Composed of microcolonies (15-20% by volume) disctributed in a shaped matrix or glycocalyx (75-80% volume) Presence of voids or water channels  Permit the passage of nutrients and other agents, acting as “circulatory” system Exopolysaccharides (EPS) – the backbone of the biofilm  50-95% of the dry weight of the biofilm  Maintain the integrity of the biofilm  Act as a buffer and a substrate for resident bacteria Physiological heterogeneity within biofilms  pH can vary quite remarkably within a biofilm  Different chemical and physical microhabitats

Supragingival dental plaque biofilm

Dental plaque in health and disease Pattern of colonization (microbial succession) in dental plaque formation Difference in predominant species  Health-associated dental plaque  Disease-associated dental plaque Dental plaque hypotheses  Specific plaque hypothesis  Non-specific plaque hypothesis

Microbiota associated with periodontal health, gingivitis, and advanced periodontal disease 0% 20% 40% 60% 80% 100% Healthy - supragingival Gingivitis crevicluar Gram-negative rods Gram-positive rods Gram-negative cocci Gram-positive cocci

Plaque reformation after cleaning

Dental plaque hypothesis Specific plaque hypothesis  A single or limited numbers of specific pathogen within dental plaque  Specific forms of periodontal disease have specific bacterial etiologies, i.e. LJP Non-specific plaque hypothesis  Overgrowth of dental plaque will lead to disease  Plaque as a relatively homogeneous bacterial mass  Gingivitis Intermediate  Qualitatively distinct bacterial composition: healthy vs. disease (subjects, sites)  Pathogenic shift; disturbed equilibrium  A small group of bacteria: Gram (-), anaerobic

Health vs. disease microflora in dental plaque Potential pathogens

Understanding dental diseases from ecological perspective The mouth - a unique microhabitat Multi-species biofilm “Selection” of “pathogenic” bacteria among microbial community  Selection pressure coupled to environmental changes Therapeutic and preventive measures - by interfering with the selection pressures responsible for their enrichment

Ecological plaque hypothesis

Dental plaque biofilm infection Ecological point of view  Ecological community evolved for survival as a whole  Complex community  Over 400 bacterial species  Adherence, coaggregation Dynamic equilibrium between bacteria and a host defense  Adopted survival strategies favoring growth in plaque  Disturbed equilibrium leading to pathology The dental plaque bacterial composition may result in a destructive inflammatory response